Method and system to manage driveline oscillations with clutch pressure control

ABSTRACT

A system and method for controlling a vehicle having an electric traction motor coupled to a transmission by a clutch include modifying torque transmitted to the driveline by modifying the clutch apply pressure in response to a difference between rotational speed of a driveline component and a filtered rotational speed of the driveline component to reduce driveline oscillation when the clutch is unlocked. The clutch pressure may be modified in response to a vehicle event that may otherwise induce driveline oscillations, such as a transmission ratio change or regenerative braking, for example.

CROSS-REFERENCE TO RELATED APPLICATIONS

This Application claims the benefit of U.S. provisional Application No.61/643,874 filed May 7, 2012, the disclosure of which is incorporated inits entirety by reference herein.

TECHNICAL FIELD

The present disclosure relates to a vehicle having an electricallypowered traction motor and a control system for controlling the vehicleusing clutch pressure to manage driveline oscillations.

BACKGROUND

Unwanted driveline oscillations may occur in many types of vehicles,including a hybrid electric vehicle (HEV) that includes an internalcombustion engine (ICE) and an electrically powered traction motor topropel the vehicle, as well as a battery electric vehicle (BEV) thatuses a battery or fuel cell to power a traction motor without an ICE.Driveline oscillations may be introduced by shifting gears, starting theengine, regenerative braking, engagement/disengagement of clutches, andvarious other disturbances. In these situations, the operator of thevehicle may experience undesirable oscillations within the cabin of thevehicle. Previous solutions to driveline oscillations include measuringa speed difference between two different driveline components to detectwindup and associated oscillation, and adjusting a torque command to theelectric motor based on that difference. There is currently a need tomore effectively manage the control of various vehicle systems to reduceor eliminate perceptible driveline oscillations.

SUMMARY

In one embodiment, a method for controlling a vehicle having a tractionmotor selectively coupled by a clutch to a driveline includes modifyingclutch pressure of the clutch in response to a difference between arotational speed of a driveline component and a filtered rotationalspeed of the driveline component to reduce driveline oscillations. Invarious embodiments, the clutch is disposed between the traction motorand a transmission and the method includes modifying the clutch pressureonly when the clutch is unlocked or slipping. The clutch may be integralwithin an automatic transmission. In one embodiment, the clutchcomprises a torque converter bypass clutch.

The driveline component may include any of a number of rotatingcomponents. In one embodiment, the driveline component comprises aninput shaft to an automatic transmission. The method may also includefiltering the rotational speed of the driveline component using a firstlow-pass filter having a cutoff frequency that varies as a function ofthe rotational speed of the driveline component. The method may alsoinclude filtering the rotational speed of the driveline component usinga second low-pass filter having a fixed calibratable cutoff frequencyhigher than the cutoff frequency of the first low-pass filter.

In various embodiments, modifying the clutch pressure includesintegrating a difference between the rotational speed and the filteredrotational speed of a driveline component. The method may includemodifying the clutch pressure in response to a difference between outputof the second low-pass filter and the integrated difference between therotational speed and the filtered rotational speed. Some embodimentsinclude an automatic transmission and modifying the clutch pressureincludes modifying the clutch pressure in response to a ratio change ofthe transmission. Modifying the clutch pressure may also be performed inresponse to activation of a vehicle regenerative braking system.

In one embodiment, a system for controlling a powertrain of a vehicleincludes a traction motor selectively coupled to a vehicle driveline bya clutch and a controller in communication with the clutch andconfigured to unlock the clutch and modify clutch pressure to controltorque transmitted to the driveline in response to a difference betweena rotational speed of a driveline component and a filtered rotationalspeed of the driveline component. In one embodiment, the controllermodifies the clutch pressure only when clutch slip is below acorresponding threshold. The controller may filter the rotational speedof the driveline component using a first low-pass filter having a cutofffrequency that varies as a function of the rotational speed of thedriveline component. The controller may also filter the rotational speedof the driveline component using a second low-pass filter having acutoff frequency higher than the cutoff frequency of the first low-passfilter.

Various embodiments according to the present disclosure include amultiple ratio automatic transmission disposed between the clutch andvehicle traction wheels as well as a disconnect clutch selectivelycoupling an internal combustion engine to the traction motor in anarrangement that may be referred to as a modular hybrid transmissionconfiguration. The system may also include a controller that modifiesthe clutch pressure when the disconnect clutch is engaged and theinternal combustion engine is started. The controller may also modifythe clutch pressure in response to a vehicle launch when the disconnectclutch is engaged, and/or in response to a ratio change of thetransmission. In some embodiments, the system includes a regenerativebraking system and the controller modifies the clutch pressure inresponse to activation of the regenerative braking system.

In one embodiment, a hybrid electric vehicle includes an engine, atraction motor selectively coupled to the engine by a first clutch, anautomatic transmission selectively coupled to the traction motor by asecond clutch, and a controller in communication with the tractionmotor, the engine, and the transmission. The controller may beconfigured to modify clutch pressure of the second clutch when thesecond clutch is unlocked in response to a difference between arotational speed of a driveline component and a filtered rotationalspeed of the driveline component. In one embodiment, the second clutchis disposed within a torque converter of the transmission.

The driveline component may include any of a number of rotatingcomponents. In one embodiment, the driveline component comprises aninput shaft of the transmission. The controller may include a firstlow-pass filter having a cutoff frequency that varies as a function ofthe rotational speed of the driveline component, and a second low-passfilter having a cutoff frequency higher than the cutoff frequency of thefirst low-pass filter.

Various embodiments according to the present disclosure provideassociated advantages. For example, driveline torque managementaccording to embodiments of the present disclosure reduces drivelineoscillations that may otherwise result from transmission ratio changes,particularly during regenerative braking of an electric or hybridelectric vehicle. However, the torque management strategy may be used inresponse to any gear change or disturbance when a vehicle launch clutchis locked, such as power-on gear changes and after engine pull-up, forexample. Systems and methods of various embodiments use rotational speedof a single driveline component, such as the traction motor, to modifytraction motor torque and improve drivability by reducing or eliminatingdriveline oscillations.

The above advantages and other advantages and features will be readilyapparent from the following detailed description of the preferredembodiments when taken in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of a powertrain system according toembodiments of the present disclosure;

FIG. 2 is a schematic representation of a transmission according toembodiments of the present disclosure;

FIG. 3 is a flow chart illustrating operation of a system or method forreducing or damping driveline oscillations according to variousembodiments of the present disclosure;

FIG. 4A is a graphical representation of traction motor speed over timewith oscillations present in the driveline;

FIG. 4B is a graphical representation of traction motor speed comparedwith a filtered motor speed according to embodiments of the presentdisclosure;

FIG. 4C is a graphical representation of a traction motor torque signaland a modified or corrected torque signal to reduce drivelineoscillations according to embodiments of the present disclosure; and

FIG. 5 is a diagram illustrating operation of a system or method formodifying traction motor torque to reduce or dampen drivelineoscillations according to embodiments of the present disclosure.

DETAILED DESCRIPTION

Detailed embodiments of the present invention are disclosed herein. Itis to be understood that the disclosed embodiments are merely exemplaryof the invention that may be embodied in various and alternative forms.The figures are not necessarily to scale; some features may beexaggerated or minimized to show details of particular components.Specific structural and functional details disclosed herein aretherefore not to be interpreted as limiting, but merely as arepresentative basis for teaching one skilled in the art to variouslyemploy the present invention. As those of ordinary skill in the art willunderstand, various features of the embodiments illustrated anddescribed with reference to any one of the Figures may be combined withfeatures illustrated in one or more other Figures to produce embodimentsthat are not explicitly illustrated or described. The combinations offeatures illustrated provide representative embodiments for typicalapplications. However, various combinations and modifications of thefeatures consistent with the teachings of the present disclosure may bedesired for particular applications or implementations. Therepresentative embodiments used in the illustrations relate generally tosystems or methods for adjusting the torque of a traction motor toreduce or eliminate oscillations in the drivetrain of an electric orhybrid electric vehicle. However, the teachings of the presentdisclosure may also be used in other applications. Those of ordinaryskill in the art may recognize similar applications or implementationswith other vehicle configurations or technologies.

Referring to FIG. 1, a representative vehicle 10 is schematically shownwith a hybrid electric drivetrain. Vehicle 10 is includes an internalcombustion engine (ICE) 12 having an output shaft 14 connected to afirst clutch implemented by disconnect clutch 16. Those of ordinaryskill in the art will recognize that driveline torque managementaccording to the present disclosure may also be used in electricvehicles that do not include an ICE. Disconnect clutch 16 drives aninput shaft 18 to an electric machine that functions primarily as atraction motor 20. Traction motor 20 may also be operated as a generatorto generate electric energy to be stored for subsequent use as generallyknown. Disconnect clutch 16 enables engine 12 and motor 20 to beselectively coupled and decoupled from one another. An output shaft 22of motor 20 is connected to a second clutch implemented by launch clutch24. Launch clutch 24 drives an input shaft 26 of a transmission 28,implemented by an automatic step-ratio gear-change transmission in oneembodiment. The launch clutch 24 may be disposed inside or outside of atransmission housing. In one embodiment, launch clutch 24 is implementedby a frictional or mechanical torque converter bypass clutch of anassociated hydrodynamic torque converter (not specifically illustrated).The present disclosure is generally independent of the particular typeof transmission, but may be particularly useful with step-ratiotransmissions that may introduce torque disturbances to the drivelinethat can contribute to driveline oscillations associated with ratiochanges of the transmission. Similar to disconnect clutch 16, launchclutch 24 enables motor 20 and transmission 28 to be selectively coupledand decoupled from one another. An output shaft of transmission 28drives a differential gear element 30, which transfers power to wheels32.

Depending on the particular application and implementation, varioustypes of electrical generation and/or storage devices may be used topower traction motor 20. In one embodiment, a high-voltage tractionbattery 34 is electrically connected to traction motor 20. Battery 34selectively supplies electric energy to drive traction motor 20, andalso selectively receives and stores electric energy from traction motor20 when traction motor 20 is acting as a generator, such as duringregenerative braking, for example. A vehicle system controller (VSC) 36and/or multiple controllers control the operation of engine 12, tractionmotor 20, and transmission 28 through electrical connection 38. Battery34 may also be electrically connected to VSC 36, and/or it may have itsown battery control module (BCM) to control charging, discharging, andvarious other battery functions.

Vehicle 10 may include a regenerative braking module or controller 90 tocontrol regenerative braking of one or more vehicle wheels 32.Regenerative braking module or controller 90 may be implemented byhardware and/or software and may be integrated within VSC 36 in someapplications and implementations. Regenerative braking may be activatedin response to various vehicle and/or ambient operating conditions orevents, such as depressing a brake pedal, releasing an acceleratorpedal, or when traveling downhill, for example.

Vehicle 10 as illustrated in the representative embodiment of FIG. 1 hasa hybrid electric drivetrain in which engine 12, motor 20, andtransmission 28 are selectively coupled in series to propel the vehicle.However, it should be understood that for purposes of the presentdisclosure, vehicle 10 may have various other powertrain configurations,such as a power split driveline, in which an engine is connected to aplanetary gear set with clutches within the transmission, and agenerator is connected to an electric motor that may power the wheels inparallel with the engine. The vehicle 10 may also be a battery electricvehicle (BEV) in which an engine is not included, and the motor 20 andbattery 34 are selectively coupled to a driveline with clutches to powerwheels 32 without an engine. Furthermore, additional components are alsocontemplated to be included in the vehicle of the present disclosure,such as a separate starter motor to start the engine 12. In short, whilethe present disclosure makes reference to a vehicle 10 with drivelinecomponents connected in series, it is contemplated that the currentdisclosure may apply to other types of vehicle drivelines that includean electric traction motor to power the wheels, with or without anengine.

The disconnect clutch 16 of the driveline selectively couples the engine12 to the motor 20. The VSC 36 and/or another controller controls thepressure of the disconnect clutch 16. When a sufficient pressure iscommanded, the disconnect clutch 16 locks and the output of the engine12 rotates at an equivalent speed with the input of the motor 20. Thisallows the engine 12 to transfer power through the motor 20 and into thetransmission 28. When a pressure less than sufficient is commanded, thedisconnect clutch 16 slips and the engine 12 may be partially orcompletely disengaged from the motor 20 so that the motor 20 cantransfer power through the transmission 28 without the losses associatedwith engine 12, thereby reducing fuel consumption. Slipping of thedisconnect clutch 16 may occur, for example, when torque output by theengine 12 is greater than an amount of power able to be withstood by thedisconnect clutch 16 based on the pressure at the disconnect clutch 16.

Similarly, the launch clutch 24 operates to engage the output of themotor 20 with the input of the transmission 28. The VSC 36 againcontrols the pressure of the launch clutch 24. The launch clutch 24 alsoslips when an amount of pressure less than full pressure is commanded bythe VSC 36. The slipping of the launch clutch 24 occurs when shaft 22 isrotating faster than shaft 26. When the launch clutch 24 is slipping,torque output of the motor 20 is not fully transferred downstream of themotor 20, but may rather be used to start the engine 12, for example, asexplained below.

In operation, the vehicle 10 may be powered by either or both of theengine 12 and the motor 20. Beginning from a stop with the engine 12off, for example, the disconnect clutch 16 may be disabled to isolatethe shafts 14, 18 from each other, the launch clutch 24 may be enabledto lock the shafts 22, 26 together, and the motor 20 may be activated tocause the wheels 32 to move. As a demand for acceleration increases, thelaunch clutch 24 may be caused to slip and the disconnect clutch 16 maybe enabled to lock the shafts 14, 18 together. The engine 12 may then bestarted and brought up to a desired speed. The amount of slipexperienced by the launch clutch 24 may then be reduced as the speed ofthe shafts 14, 18, 22 approaches the speed of the shaft 26 and theoutput shaft of the transmission 28.

The VSC 36 receives information from one or more sensors (not shown)placed throughout the driveline. The VSC 36 can monitor rotationalspeeds of the engine 12, the motor 20, and other components in thedriveline such as shafts 14, 18, 22, 26, and the axle shaft thatconnects the differential gear element 30 to the wheels 32. When thelaunch clutch 24 is locked and not slipping, a rotational speed of anydriveline component on the output side of the motor 20 indicates therotational speed of the motor 20, after gear ratio calculations. Whenthe launch clutch 24 is slipping, the rotational speed of any drivelinecomponent downstream of shaft 26 indicates the speed of the vehicleafter gear ratio calculations, while the rotational speeds of shafts 18,22 indicate rotational speed of the motor 20. In such a scenario, therotational speeds of shafts 18, 22 may differ from the rotational speedof shaft 26.

Referring to FIG. 2, the transmission 28 is shown in detail, along withother vehicle components. The transmission 28 is driven by the inputshaft 26 that receives torque from the engine 12 and/or the motor 20through the use of clutches 16, 24, as previously described. Thetransmission input shaft 26 is operatively connected to a first portion44 of a forward clutch (FC) 46. The first portion 44 of the forwardclutch 46 is also the first portion of a direct clutch (DC) 48. Theforward clutch 46 and the direct clutch 48 each have respective secondportions 50, 52 which are operatively connected to a respective torqueelement within the transmission 28.

The second portion 50 of the forward clutch 46 is operatively connectedto a first sun gear (S1) 54. The second portion 52 of the direct clutch48 is operatively connected to a first ring gear (R1) 56. A firstplanetary gear set includes the first sun gear 54, the first ring gear56, and a first planetary carrier (P1) 58. The first planetary gear setis operatively connected to a second planetary gear set. The secondplanetary gear set includes a second sun gear (S2) 60, a second ringgear (R2) 62, and a second planetary carrier (P2) 64. The secondplanetary carrier 64 is connected to the first ring gear 56 of the firstplanetary gear set, and also to a low-and-reverse brake (L/R) 66. Thesecond sun gear 60 is connected to a reverse clutch (RC) 68 which mayinclude a friction brake 70. The reverse clutch 68 is also operativelyconnected to the transmission input shaft 26.

The ring gear 62 defines a sprocket for a chain drive, indicatedgenerally at 72. The chain drive 72 drives a sprocket 74, which in turn,drives a third sun gear (S3) 76 of a third planetary gear set. The thirdplanetary gear set also includes a third ring gear (R3) 78 and a thirdplanetary carrier (P3) 80. The ring gear 78 is grounded to thetransmission housing, while the planetary carrier 80 is attached to thedifferential gear element 30. The differential gear element 30 transferstorque to wheels 32, as described previously with reference to FIG. 1.

FIG. 2 illustrates a launch clutch 24 between the transmission 28 andthe motor 20. It should be understood that clutches 46 and 48 within thetransmission 28 may be present in place of, or in combination with,launch clutch 24. FIG. 2 shows all clutches 24, 46 and 48 together as anillustration of possible clutch locations that all work to selectivelycouple the motor 20 to the transmission 28 and allow for slip so thatthe motor 20 can work to start the engine 12 and power the wheels 32. Itshould be understood that slipping may be commanded to forward clutch 46for the same purposes as slipping the launch clutch 24. The slippingdescribed in this disclosure in regards to launch clutch 24 is not meantto be limited to only launch clutch 24, but may also apply to clutches46 and 48 depending on the configuration of the driveline and thetransmission 28.

Referring to FIGS. 1 and 2, when the VSC 36 commands a start of theengine 12 to provide torque to the wheels, a command is given to thelaunch clutch 24 to reduce pressure in the clutch 24 to allow the clutch24 to slip. If the launch clutch 24 is already slipping when the VSCcommands a start of the engine 12, pressure can be further reduced toallow the clutch 24 to further disengage and allow for more slip. Oncesufficient slipping of the launch clutch 24 is present, the disconnectclutch 16 is engaged and the motor 20 rotates the engine 12 to bring itup to speed so that it may begin to combust fuel and provide torque. Bypartially disengaging the launch clutch 24 during engine start, thevehicle driveline, including the vehicle wheels 32, is at leastpartially isolated from engine torque disturbances, so that starting theengine 12 may go unnoticed by a vehicle occupant. Similarly, when theengine 12 is requested to stop, the VSC 36 commands a pressure reductionin the disconnect clutch 16 to disengage the engine 12 from the motor20. The motor 20 may then provide sufficient torque requests to thewheels 32 until power demand increases to a level in which the engine 12must start again.

During operation, the driveline of the vehicle 10 may experienceunwanted oscillations. For example, when shifting between gears,circumstances may exist that excite an oscillation of the output shaft22 of the motor 20. These oscillations may increase to a level that isfelt within the cabin of the vehicle and noticed by a vehicle occupant.A solution to dampen and combat these oscillations is provided withreference to FIGS. 3-5.

Referring to FIG. 3, a high level flowchart illustrates a system andmethod to dampen driveline oscillations in accordance with the presentdisclosure. At 100, the VSC or other controller receives a signalindicative of a rotational speed of a driveline component. The drivelinecomponent may be one of the shafts 14, 18, 22, 26, the output shaft ofthe transmission, the shafts of the axle to the wheels 32, or the motor20. When launch clutch 24 is locked and there is no slip, a rotationalspeed of any driveline component downstream of the motor 20 can indicatethe rotational speed of the motor 20 itself after taking into accountgear ratios. Similarly, if the disconnect clutch 16 is locked and thereis no slip, the rotational speed of the motor 20 can be indicated by therotational speed of any driveline component between the engine 12 andthe motor 20. Therefore, the rotational speed of the motor 20 can bedetermined by measuring the rotational speed of any driveline component.The speed of any driveline component may be measured while the launchclutch 24 is slipping or not slipping. However, if the speed is measuredof a component downstream of the motor 20 (for example, transmissioninput shaft 26) while the launch clutch 24 is slipping, then the speedof the motor 20 may only be determined if the amount of clutch pressureis known.

At 102, the rotational speed of the driveline component is filtered. Thefiltering is described in further detail with respect to FIGS. 4B and 5,however a high level chart is illustrated in FIG. 3. The filtering at102 may include sub-steps 104, 106 and 108. First, at 104, therotational speed is filtered by a time-delayed adjustable rate filter.This yields a filtered rotational speed that reduces oscillating motorspeed values. At 106, the difference between the filtered speed and theactual speed is integrated. This, multiplied by some gain, yields acorrection factor. At 108, the correction factor is added to thefiltered rotational speed, thus yielding a corrected desired motorspeed. The corrected desired motor speed represents the desired speed ofthe motor without unwanted oscillations.

At 110, an error signal is created by subtracting the corrected desiredmotor speed from the actual rotational speed. This error signal may bemultiplied by a gain to obtain a corrected torque value, as will bediscussed.

At 112, it is determined whether or not the launch clutch 24 isslipping. This may be determined by any of a number of strategies,including comparing the speeds of the motor output shaft 22 and thetransmission input shaft 26, measuring the pressure on the clutch 24, orby determining if the VSC 36 has commanded the launch clutch 24 to slipor to not slip. This determination of whether the launch clutch 24 isslipping is for the purposes of deciding how to alter torque to thewheels 32 to dampen the driveline oscillations. If the launch clutch 24is slipping, at 114, the VSC 36 sends a pressure command signal to alterthe pressure of the launch clutch 24. By altering the pressure of thelaunch clutch 24, the torque at the wheels 32 is consequently altered.Likewise, if the launch clutch 24 is not slipping, at 116, the VSC 36sends a torque command signal to the motor 20 to alter the motor torque.Because the launch clutch 24 is not slipping, the adjustment of thetorque of the motor 20 to correspond to the oscillations of thedriveline consequently alters the torque transmitted to the wheels 32.The system returns at 118 to continuously monitor and dampen drivelineoscillations throughout operation of the vehicle.

Referring to FIGS. 4A-C, the filtering and torque adjustment isgraphically illustrated. Reference herein is made to motor speedoscillations. However, it should be understood that measuring motorspeed may be advantageous only in the case of when the launch clutch 24is not slipping because rotational speed anywhere along the drivelineindicates rotational speed of the motor 20. It may be advantageous tobase the torque adjustment on the rotational speed of the input shaft 26of the transmission 28 when the launch clutch 24 is slipping, asincreasing the torque of the motor 20 when the launch clutch 24 isslipping may not adequately adjust torque at the wheels 32. Therefore,in the case in which the launch clutch 24 is slipping while drivelineoscillations are present, the illustrations of FIGS. 4A-C can illustrateto measurements of the rotational speed of the input shaft 26 ratherthan the rotational speed of the motor 20. It is therefore contemplatedthat the measurement of rotational speed and torque/clutch adjustmentsmade in response thereto may occur at any driveline component, butreference is made to a motor speed in FIGS. 4A-C for simplicity.

FIG. 4A shows motor speed versus time, indicated at 200. As the motorspeed 200 decreases after a gear shift, for example, oscillations in themotor speed exist. As explained previously, this may result in unwantedvibrations experienced by an operator of the vehicle. This is oneillustration of driveline oscillations; it is also contemplated thatdriveline oscillations and the corresponding dampening system may beadvantageous in many other situations, for example, as the motor speed200 is increasing. It is also contemplated that motor speed requestsignals sent to the motor may undergo light filtering to eliminatespikes of motor speed, and this light filtering is a product thatresults in the actual motor speed 200 versus time in FIG. 4A. FIGS. 4Band 4C focus on the oscillating segment of the motor speed 200 of FIG.4A.

FIG. 4B illustrates the filtering system as previously described withreference to steps 102-110 of FIG. 3. A more detailed description isprovided with reference to the algorithm illustrated in FIG. 5.Referring to FIGS. 3 and 4B, the measured speed 200 of the motor 20 isshown. The motor speed 200 is then filtered to essentially yield anaverage or mean of previous values of rotational speed. A plot of thisfiltered rotational speed 202 represents a smoothed, time-delayed plotcompared to a plot of the actual motor speed 200. At step 106, thedifference between the filtered motor speed 202 and the actual motorspeed 200 is integrated to compute a correction factor 206. Thiscorrection factor 206 is then added to the filtered speed 202 toeffectively shift the filtered motor speed 202. The shifted filteredmotor speed represents a smoothed motor speed that is not time-delayedfrom the actual motor speed. This may be referred to as the “correcteddesired motor speed” 208.

Once the corrected desired motor speed 208 is determined, the torque ofthe motor or the pressure of the clutch can be adjusted, depending onwhether or not the launch clutch 24 is slipping, as describedpreviously. To do so, an error or difference signal 210 is created. Theerror or difference signal 210 is defined by the difference between thecorrected desired motor speed 208 and the actual motor speed 200. Theerror signal 210 is multiplied by a gain to convert the error signalinto a torque correction signal (FIG. 4C). This torque correction signalis added to the torque demand of the motor 20 or the launch clutch 24,again depending on whether or not the launch clutch 24 is slipping.

Referring to FIG. 4C, motor torque (or clutch pressure in oneembodiment) without damping 212 is shown in comparison with thecommanded motor torque/clutch pressure with damping 214. Thetorque/clutch correction is added to (or subtracted from) the originaltorque/clutch request of the motor/clutch to create a new torque/clutchpressure request 214 to dampen oscillations. The new dampenedtorque/clutch pressure request 214 is received by the motor 20 or thelaunch clutch 24, which in turn alters the final torque received at thewheels 32. Altering the torque (or clutch pressure in one embodiment)based upon a difference between a rotational speed of a drivelinecomponent and a filtered rotational speed of the driveline componentthus dampens driveline oscillations perceived by an occupant of thevehicle.

Referring to FIG. 5, the filtering method of step 102 and correspondingillustrations of FIGS. 4B-4C will now be described in further detail.Reference numbers in FIG. 5 correspond to the signals of FIGS. 4A-4C.While references in FIG. 5 may be made to a measurement of a motorspeed, it may be beneficial to instead measure the speed of the inputshaft 26 in an embodiment in which the launch clutch 24 is slipping. Inthe situation in which the launch clutch 24 is slipping, torqueadjustments may be carried out by adjusting the clutch pressure ratherthan the motor torque, as previously described.

First, the speed of the motor 20 or other driveline component ismeasured at 200. The measured speed 200 is low-pass filtered by aninfinite impulse response filter 201. The filter 201 has a cutofffrequency that depends on the value of the measured speed 200, withhigher measured speeds having less filtering. The filter 201 may, forexample, have a filter output value defined as:Filter_(output)=k*ω_(motor)+(1−k)*Past_Filter_(Outputs), where k is anadjustable value as a function of the motor speed ω_(motor). The outputof the filter 201 is a smoothed representation of the speed of the motor20, but is uncorrected in that it is shifted in mean value from thespeed of the motor 20 due to time delay caused by the filtering at 201.

To restore the mean value of the uncorrected filtered speed 202, thedifference 203 between the measured speed 200 and the uncorrectedfiltered speed 202 is integrated at 204. The result of the integrationis the mean restoring correction factor 206. The correction factor 206is added to the uncorrected filter speed 202 to result in the correcteddesired motor speed 208.

To alter the torque of the vehicle based on the corrected desired motorspeed 208, the measured speed 200 is low-pass filtered by a secondinfinite impulse response filter 209. The filter 209 has a cutofffrequency that has a calibration constant substantially higher than thecutoff frequency of the first filter 201. The output of the filter 209is subtracted from the corrected desired motor speed 208 to create aspeed error signal 210. The error signal 210 is proportional to thedisturbances caused by the driveline oscillations. The error signal 210is then limited in authority at 211 before being added to the desiredmotor torque 212 (or desired clutch pressure), thus changing the motortorque command 212 (or clutch pressure command). The changed motortorque command 212 (or clutch pressure command) results in a torquecommand signal (or clutch pressure command signal) that includesdamping, shown at 214.

As such, various embodiments according to the present disclosure providedriveline torque management to reduce or eliminate drivelineoscillations that may otherwise result from transmission ratio changes,particularly during regenerative braking of an electric or hybridelectric vehicle. The torque management strategy may be used in responseto any gear change or disturbance when a vehicle launch clutch islocked, such as power-on gear changes and after engine pull-up, forexample. In addition, various embodiments use rotational speed of only asingle driveline component, such as the traction motor, to modifytraction motor torque and improve drivability by reducing or eliminatingdriveline oscillations.

While the best mode has been described in detail, those familiar withthe art will recognize various alternative designs and embodimentswithin the scope of the following claims. While various embodiments mayhave been described as providing advantages or being preferred overother embodiments with respect to one or more desired characteristics,as one skilled in the art is aware, one or more characteristics may becompromised to achieve desired system attributes, which depend on thespecific application and implementation. These attributes include, butare not limited to: cost, strength, durability, life cycle cost,marketability, appearance, packaging, size, serviceability, weight,manufacturability, ease of assembly, etc. The embodiments describedherein that are described as less desirable than other embodiments orprior art implementations with respect to one or more characteristicsare not outside the scope of the disclosure and may be desirable forparticular applications.

What is claimed is:
 1. A method for controlling a vehicle having atraction motor selectively coupled by a clutch to a driveline,comprising: modifying clutch pressure of the clutch in response to adifference between a rotational speed of a driveline component and afiltered rotational speed of the driveline component to reduce drivelineoscillations.
 2. The method of claim 1 wherein the clutch is disposedbetween the traction motor and a transmission, wherein the methodcomprises modifying the clutch pressure only when the clutch is notlocked.
 3. The method of claim 1 wherein the clutch is integral within atransmission.
 4. The method of claim 3 wherein the clutch comprises atorque converter bypass clutch.
 5. The method of claim 1 wherein thedriveline component comprises an input shaft to a transmission.
 6. Themethod of claim 1 further comprising: filtering the rotational speed ofthe driveline component using a first low-pass filter having a cutofffrequency that varies as a function of the rotational speed of thedriveline component.
 7. The method of claim 6 further comprising:filtering the rotational speed of the driveline component using a secondlow-pass filter having a fixed calibratable cutoff frequency higher thanthe cutoff frequency of the first low-pass filter.
 8. The method ofclaim 7 wherein modifying the clutch pressure includes integrating adifference between the rotational speed and the filtered rotationalspeed, the method further comprising: modifying the clutch pressure inresponse to a difference between output of the second low-pass filterand the integrated difference between the rotational speed and thefiltered rotational speed.
 9. The method of claim 1 wherein the vehicleincludes a transmission and wherein modifying the clutch pressurecomprises modifying the clutch pressure in response to a ratio change ofthe transmission.
 10. The method of claim 1 wherein modifying the clutchpressure comprises modifying the clutch pressure in response toactivation of a vehicle regenerative braking system.
 11. A system forcontrolling a powertrain of a vehicle, comprising: a traction motorselectively coupled to a vehicle driveline by a clutch; and a controllerin communication with the clutch and configured to unlock the clutch andmodify clutch pressure to control torque transmitted to the driveline inresponse to a difference between a rotational speed of a drivelinecomponent and a filtered rotational speed of the driveline component.12. The system of claim 11 wherein the controller modifies the clutchpressure only when clutch slip is below a corresponding threshold. 13.The system of claim 11 wherein the controller filters the rotationalspeed of the driveline component using a first low-pass filter having acutoff frequency that varies as a function of the rotational speed ofthe driveline component.
 14. The system of claim 13 wherein thecontroller filters the rotational speed of the driveline component usinga second low-pass filter having a cutoff frequency higher than thecutoff frequency of the first low-pass filter.
 15. The system of claim11 further comprising: a multiple ratio transmission disposed betweenthe clutch and vehicle traction wheels; and a disconnect clutchselectively coupling an internal combustion engine to the tractionmotor.
 16. The system of claim 15 wherein the controller modifies theclutch pressure when the disconnect clutch is engaged and the internalcombustion engine is started.
 17. The system of claim 15 wherein thecontroller modifies the clutch pressure in response to a vehicle launchwhen the disconnect clutch is engaged.
 18. The system of claim 15wherein the controller modifies the clutch pressure in response to aratio change of the transmission.
 19. The system of claim 15 furthercomprising a regenerative braking system, wherein the controllermodifies the clutch pressure in response to activation of theregenerative braking system.
 20. A hybrid electric vehicle, comprising:an engine; a traction motor selectively coupled to the engine by a firstclutch; an automatic transmission selectively coupled to the tractionmotor by a second clutch; and a controller programmed to modify clutchpressure of the second clutch when the second clutch is unlocked inresponse to a difference between a rotational speed and a filteredrotational speed of the driveline component.
 21. The vehicle of claim 20wherein the second clutch is disposed within a torque converter of thetransmission.
 22. The vehicle of claim 20 wherein the drivelinecomponent comprises an input shaft of the transmission.
 23. The vehicleof claim 20 wherein the controller comprises: a first low-pass filterhaving a cutoff frequency that varies as a function of the rotationalspeed of the driveline component; and a second low-pass filter having acutoff frequency higher than the cutoff frequency of the first low-passfilter.